If I need to re-establish the MBR to point to GRUB, I type the following at
the grub prompt:

grub> root (hd0,0)
 Filesystem type is ext2fs, partition type 0x83

grub> setup --prefix=/grub/i386-redhat (hd0)
 Checking if "/grub/i386-redhat/stage1" exists... yes
 Checking if "/grub/i386-redhat/stage2" exists... yes
 Checking if "/grub/i386-redhat/e2fs_stage1_5" exists... yes
 Running "embed /grub/i386-redhat/e2fs_stage1_5 (hd0)"...  16 sectors are 
   embedded.
succeeded
 Running "install /grub/i386-redhat/stage1 d (hd0) (hd0)1+16 p 
(hd0,0)/grub/i386-redhat/stage2 /grub/i386-redhat/grub.conf"... succeeded
Done.

grub> quit


Notice that the file the standard setup command uses is 
/grub/i386-redhat/grub.conf, which doesn't exist!  This file, IIRC, used to
be named menu.1st.  Regardless, the name doesn't matter as much as the
location.  It (the location) is correct by grub standards, but not for Red
Hat.  The installer creates the grub.conf file in /boot/grub/grub.conf.

To solve the descrepency you should use one location or the other... make
grub default to using our /boot/grub/grub.conf location, or make the
installer use the /boot/grub/i386-redhat/grub.conf location.  Maybe an easy
way out is to make /boot/grub/i386-redhat/grub.conf a hard link to
/boot/grub/grub.conf (?)

Thank you,

Joshua Jensen